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I'm looking for a two-player board game I played 20-25 years ago (in the Netherlands). The board is upright, as if it's kind of a wall, and players are sitting on opposite sides of the wall, not seeing each other's boards. The objective is to get small 'coins' from the top of the board to the bottom; the first player to do so wins. One player has red coins, the other one yellow. There are (blue, IIRC) wheels of various sizes in the wall; players take turns rotating these wheels. The wheels have 3-5 small cavities, evenly spaced, to hold the coins. The coins stay in the wheel because the rest of the wall holds them there, except for a few tunnels where they can fall to the next wheel. I think you cannot see where the cavities at your opponent's side are, this is the hidden information which makes the game interesting. Whenever you rotate a wheel to improve your own position, you might accidentally help your opponent forward as well.

This is a rough sketch of how a part of the board looks like:

In dutch it was called "onderuit". Also known as downspin.

There where several discs that could be replaced to make the game harder or simpler. The later versions of the game worked with keys (one for each player) to avoid turning one disk when your opponent has just turned it. The early versions could be turned without key.

As far as I know, the board was blue and the disks where white. There where 4 sets of coins (4 colors) each player had to dock 2 sets. And they where numbered. So you could rule that you had to dock them in order to make the game harder.